Abstract

We have previously demonstrated that neutrophil recruitment to the heart following myocardial infarction (MI) is enhanced in mice lacking 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) that regenerates active glucocorticoid within cells from intrinsically inert metabolites. The present study aimed to identify the mechanism of regulation. In a mouse model of MI, neutrophil mobilization to blood and recruitment to the heart were higher in 11β-HSD1-deficient (Hsd11b1-/- ) relative to wild-type (WT) mice, despite similar initial injury and circulating glucocorticoid. In bone marrow chimeric mice, neutrophil mobilization was increased when 11β-HSD1 was absent from host cells, but not when absent from donor bone marrow-derived cells. Consistent with a role for 11β-HSD1 in 'host' myocardium, gene expression of a subset of neutrophil chemoattractants, including the chemokines Cxcl2 and Cxcl5, was selectively increased in the myocardium of Hsd11b1-/- mice relative to WT. SM22α-Cre directed disruption of Hsd11b1 in smooth muscle and cardiomyocytes had no effect on neutrophil recruitment. Expression of Cxcl2 and Cxcl5 was elevated in fibroblast fractions isolated from hearts of Hsd11b1-/- mice post MI and provision of either corticosterone or of the 11β-HSD1 substrate, 11-dehydrocorticosterone, to cultured murine cardiac fibroblasts suppressed IL-1α-induced expression of Cxcl2 and Cxcl5 These data identify suppression of CXCL2 and CXCL5 chemoattractant expression by 11β-HSD1 as a novel mechanism with potential for regulation of neutrophil recruitment to the injured myocardium, and cardiac fibroblasts as a key site for intracellular glucocorticoid regeneration during acute inflammation following myocardial injury.

Cultured cardiac fibroblast expression of Hsd11b1, Cxcl2, Cxcl5 and Il-6 in the presence or absence of IL-1α ± Cort or DHC. (A) qPCR analysis of Cxcl2 and Cxcl5 in cardiac fibroblasts cultured in the presence or absence of IL-1α for 24 h. (B) qPCR carried out on cardiac fibroblasts in the presence or absence of IL-1α ± corticosterone (Cort) or 11-DHC, expressed as fold change over IL-1α treatment alone. Protein production of CXCL2 (C) and CXCL5 (D) in the supernatants as measured by ELISA. (E) The influence of IL-1α ± corticosterone (Cort) or 11-DHC on expression of Il-6 by cultured mouse cardiac fibroblasts. *P < 0.05, **P < 0.01, ***P < 0.005. n = 3–5 per group.

Schema for the regulation of neutrophil recruitment to the heart by 11β-HSD1. (A) Chemokines produced by fibroblasts in response to pro-inflammatory cytokines recruit neutrophils to the heart post MI (1). Thy1high and Thy1low cardiac fibroblasts preferentially produce CXCL2 and CXCL5, respectively (2). 11β-HSD1 catalyzes the regeneration of local glucocorticoid, dampening chemokine expression (3). Circulating corticosterone and IL-1α from necrotic cardiomyocytes increase 11β-HSD1 expression (4). (B) In the absence of 11β-HSD1, fibroblasts are driven to produce excess CXCL2 and CXCL5 (5), unleashed due to the lack of dampening local glucocorticoid (6), driving increased neutrophil recruitment to the infarcted heart (7).